The invention concerns a composite ceramic body, especially designed for a tribological component such as a brake disk, including a fiber-reinforced carbon-containing core area as well as a SiC-containing surface area. The invention concerns also a process for producing a fiber-reinforced composite ceramic body, especially designed for a tribological component such as a brake disk, wherein a carbon body containing fibers is infiltrated with silicon, and the body is ceramicized by initiating a chemical reaction while forming SiC.
From DE 198 34 571 C2 is known a process for producing bodies from fiber-reinforced C/C preforms having a porous carbon matrix, in which the preform that is fiber-reinforced by pyrolisis is infiltrated with molten silicon. The liquid silicon can thus become embedded in the pores to produce the desired hardness in the surface layer of the CMC (ceramic matrix composite material) produced in this way.
In DE 44 38 455 C1 is described a process for producing a friction unit by infiltrating a porous carbon body with liquid silicon, wherein the porous carbon body is structured in such a way that hollow spaces and/or recesses are formed in defined interior and/or outer spaces which retain their shape and size after ceramization.
Corresponding bodies consisting of CMC materials can be used for brake disks, such as those described in DE 42 37 655 A1 or EP 071 214 B1.
From JP 0003199172 AA is known a coated carbon-fiber reinforced composite material, wherein the carbon fibers are available in a matrix, whose central part consists of carbon and whose surface consists of carbides. The transition from interior to exterior runs thus continuously or almost continuously exclusively in the surface area.
DE 198 05 868 A1 concerns a process for producing a fiber composite material, in which is used a fiber coating whose quality is increased from the exterior toward the interior to obtain a gradient material. Molding compounds of different coating quality, whose outer layers can consist entirely of silicon carbide, are introduced into a pressing die for this purpose. Furthermore, the fiber quality as well as fiber length can vary. The used reinforcing fibers themselves consist of a core having a coating of pyrocarbon and an external layer of pyrolyzable binding material that is converted into carbon by pyrolisis. An infiltration with liquid silicon can take place.
The CMC brake disks used today have an outer, almost monolithic SiC layer (surface area) in addition to a core area (core laminate). This surface layer is required due to tribological reasons. Instead, the core area should have CFC properties in order to attain if possible an almost ductile fracture failure of the overall system. According to the current state of development, the layer structure is such that a pronounced layer transition from the monolithic surface area structure to the CFC core area exists. Great differences in the mechanical and thermophysical properties arise because of this. Optically, it can be perceived in the corresponding layer system, that the monolithic layer is not only highly cracked, but has a tendency to further crack formation during use.